1. Field of the Invention
The present invention relates to a method for manufacturing golf club heads and more particularly to a method for manufacturing metal golf club heads such as iron club heads and metal-wood club heads.
2. Prior Art
Some conventional golf club heads of irons and metal-woods are obtained from a ball-striking part and a hosel part (called "hosel") which are two independent pieces formed separately from different materials and then joined into an integral unit. This type of club head is disclosed in, for instance, Japanese Patent Application Laid-Open (Kokai) No. H8-215350 which was filed by the applicant of the present patent application.
In this prior art which is described for an iron club head, the overall weight of the head is lightened, the center of gravity is lowered, and the cost of the head is reduced by use of a metal material having a relatively large specific gravity such as carbon steel (Fe), stainless steel (SUS), a beryllium-copper alloy (Be--Cu), tungsten carbide (WC) or the like for the ball-striking member and a metal material having a relatively small specific gravity such as titanium (Ti), a titanium alloy, aluminum (Al), an aluminum alloy or the like for the hosel. Because of these materials, the hosel can be endowed with interchangeability; and as a result, it is possible to make variations in terms of ball-striking performance and external appearance.
In the golf club having a head as described above, the ball-striking part and the hosel are brought together under a convex-concave type interlocking relationship between the joining end surface of the ball-striking part and the joining end surface of the hosel, and then the outer circumference of the joint boundary area between the two members are welded. However, such an interlocking relationship of the ball-striking part and hosel would not necessarily provide a perfectly aligned engagement between the two. In addition, since only the outer circumference of the joint boundary area between the two members is welded, the welded area tends to locate only at the circumferential edges of the respective joining end surfaces and would not extend throughout the interior portions of the joint portion. Thus, the above joining method does not provide a complete joint structure.
As a result, it is likely that the welded area between the ball-striking part and the hosel can be destroyed by the impact of striking the ball during long-term repeated use, and the two members become loosened, causing a danger that the ball-striking part may fall off of the hosel.